Plant physiology
At the smallest scale are molecular interactions of photosynthesis and internal diffusion of water, minerals, and nutrients.
To function and survive, plants produce a wide array of chemical compounds not found in other organisms.
Many flowering plants bloom at the appropriate time because of light-sensitive compounds that respond to the length of the night, a phenomenon known as photoperiodism.
The ripening of fruit and loss of leaves in the winter are controlled in part by the production of the gas ethylene by the plant.
The chemical elements of which plants are constructed—principally carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, etc.—are the same as for all other life forms: animals, fungi, bacteria and even viruses.
Despite this underlying similarity, plants produce a vast array of chemical compounds with unique properties which they use to cope with their environment.
Perhaps the most celebrated compounds from plants are those with pharmacological activity, such as salicylic acid from which aspirin is made, morphine, and digoxin.
Drug companies spend billions of dollars each year researching plant compounds for potential medicinal benefits.
Chlorophyll is the primary pigment in plants; it is a porphyrin that absorbs red and blue wavelengths of light while reflecting green.
They function as accessory pigments in plants, helping to fuel photosynthesis by gathering wavelengths of light not readily absorbed by chlorophyll.
They occur in all tissues of higher plants, providing color in leaves, stems, roots, flowers, and fruits, though not always in sufficient quantities to be noticeable.
This class of pigments is found only in the Caryophyllales (including cactus and amaranth), and never co-occur in plants with anthocyanins.
[3] Plants produce hormones and other growth regulators which act to signal a physiological response in their tissues.
They also produce compounds such as phytochrome that are sensitive to light and which serve to trigger growth or development in response to environmental signals.
Plant hormones are chemicals that in small amounts promote and influence the growth, development and differentiation of cells and tissues.
The UV-B receptor is one or more compounds not yet identified with certainty, though some evidence suggests carotene or riboflavin as candidates.
Conversely, short day plants flower when the length of daylight falls below a certain critical level.
Day neutral plants do not initiate flowering based on photoperiodism, though some may use temperature sensitivity (vernalization) instead.
This fact is utilized by florists and greenhouse gardeners to control and even induce flowering out of season, such as the poinsettia (Euphorbia pulcherrima).
Whatever name is applied, it deals with the ways in which plants respond to their environment and so overlaps with the field of ecology.
Of particular importance are water relations (which can be measured with the Pressure bomb) and the stress of drought or inundation, exchange of gases with the atmosphere, as well as the cycling of nutrients such as nitrogen and carbon.
[6] Nevertheless, the plant kingdom as a whole do not feel pain notwithstanding their abilities to respond to sunlight, gravity, wind, and any external stimuli such as insect bites, since they lack any nervous system.
Nastic movements results from differential cell growth (e.g. epinasty and hiponasty), or from changes in turgor pressure within plant tissues (e.g., nyctinasty), which may occur rapidly.
Plant are susceptible to the same kinds of disease organisms as animals, including viruses, bacteria, and fungi, as well as physical invasion by insects and roundworms.
In some cases, a plant can simply shed infected leaves or flowers to prevent the spread of disease, in a process called abscission.
One of the most important advances in the control of plant disease was the discovery of Bordeaux mixture in the nineteenth century.
Application of the mixture served to inhibit the growth of downy mildew that threatened to seriously damage the French wine industry.
Jan Baptist van Helmont published what is considered the first quantitative experiment in plant physiology in 1648.
[11] Researchers discovered in the 1800s that plants absorb essential mineral nutrients as inorganic ions in water.
This observation is the basis for hydroponics, the growing of plants in a water solution rather than soil, which has become a standard technique in biological research, teaching lab exercises, crop production and as a hobby.
